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|United States Patent
,   et al.
February 8, 1994
Natural gamma ray logging sub
A natural gamma tag marking materials for sub or permanent markers used in
gamma logging operations, such natural gamma materials having a gamma
count of between 200 and 1000 counts per second. The instant invention
further discloses a typical Sub, for insertion in a drilling operation,
utilizing natural gamma element compounds which are considered to be
non-hazardous and effective as tag markers when used in wireline logging
Daigle; Robert A. (108 Winbourne, Scott, LA 70583);
Tumlin; Dave M. (1037 Jolie Blonde Rd., Breaux Bridge, LA 70517)
August 17, 1992|
|Current U.S. Class:
||250/303; 250/260; 378/60 |
|Field of Search:
U.S. Patent Documents
|4436996||Mar., 1984||Arnold et al.||250/256.
Primary Examiner: Anderson; Bruce C.
Attorney, Agent or Firm: Montgomery; Robert N.
What is claimed is:
1. A natural gamma count emitting tag marking sub, comprising:
a) a threaded body, having a box end with internal tapered threads and a
pin end with external tapered threads, for threadably coupling into a
down-hole tubing string; and
a natural gamma emitting compound, having a gamma count between 200 and
1000 counts per second, contained within said threaded body.
2. A natural gamma tagging sub as defined in claim 1 wherein said natural
gamma material is a hydroxide or nitrate taken from a compound whose
primary element is chosen from the group consisting of potassium, thorium,
3. A natural gamma tagging sub as defined in claim 1 wherein said threaded
body further comprises: an inner sleeve, threadably secured therein having
a sealing means at either end and a recessed portion therebetween, for
containing said natural gamma emitting compound.
4. A natural gamma tagging sub as defined in claim 3 wherein said sealing
means is an o-ring located at each end of said inner sleeve.
5. A natural gamma tagging sub as defined in claim 3 wherein said inner
sleeve is purged of air during installation with said threaded body by
submerging in oil.
6. A natural gamma count emitting tag marking sub, comprising
a) a body, having a box end with internal tapered threads and a pin end
with external tapered threads, for threadably coupling into a down-hole
b) an inner sleeve, threadably secured within said box end;
c) a natural gamma emitting compound, having a gamma count between 200 and
1000 counts per second, contained between the walls of said body and said
7. A natural gamma tagging sub as defined in claim 6 wherein said body's
inner sleeve further comprises:
a) a tubular, having external threads at one end;
b) an external sealing means, adjacent said external threads and at the
opposite end, for sealing said inner sleeve within said body;
c) a recessed portion, located between said sealing means; and
d) mating notches, located internally at the externally threaded end of
said tubular for removal of said inner sleeve.
8. A natural gamma tagging sub as defined in claim 7 wherein said sealing
means is an o-ring located at each end of said inner sleeve thereby
forming a recess therebetween.
9. A natural gamma tagging sub as defined in claim 8 wherein said cavity is
purged of air when said body and said inner sleeve are threadable engaged
while submerged in oil.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a gamma radiation emitting tool joint referred to
as a sub, often used in wireline logging operations as tag markers or
permanent reference points in conjunction with tubing conveyed drilling
tools etc. More particularly, the present invention is directed to an
improved material and method of conveyance for performing such task.
2. General Background
Radioactive tag markers utilized in a drilling operation are by no means
new. However, they have evolved over the years, from permanent markers
placed in the casing or tubing, to cobalt pellets implanted into a
drilling tube sub. These reference markers are necessary to provide an
exact known location for perforating and other such down hole operations.
Although each joint of drill pipe or tubing is measured prior to insertion
in the bore hole, even small measurement errors and coupling differences
become cumulative over the hundreds of joints of pipe used in the string,
resulting in errors of several feet in some cases. Stretch and bounce in
the wireline while logging the well also plays a large role in drilling
tool location error. Therefore, it has been the accepted practice to
provide a highly radioactive substance as a detectable tag marker
referencing source, located in the near vicinity of the tool joint. Thus,
when the initial subsurface formation log is compared to a through tubing
wireline log, for any given well, in which a tag marking reference source
has been placed near the tool joint, a high gamma count spike is
detectable and can be accurately located utilizing the standard API gamma
ray tubing collar locator scale.
It has been assumed in the past that the radioactive tag marker reference
source must have a high gamma count to overcome the natural gamma
radiation being emitted by the surrounding subsurface formations.
Therefore, high gamma count elements such as cobalt with gamma counts in
excess of 3600 counts/sec. are currently being used. High radiation
elements, when used in well logging operations, are highly controlled by
the Nuclear Regulatory Commission, the Department of Transportation and
various environmental agencies, both Federal and State. Personnel must be
highly trained and a paper trail must be maintained at all times for the
handling of such materials to minimize human exposure to radiation. A
license must also be acquired and maintained for each state through which
the material passes and expensive equipment must be utilized in the
handling and detection process. The necessary equipment can not be
transported quickly by air, if at all, due to these time consuming
restrictions. Accordingly, there is a need for a gamma ray tag marker that
can be detected by the wireline logging operation which does not exhibit
the draw backs hereabove mentioned. Namely, a less hazardous substance
that can be handle without risk to personnel.
SUMMARY OF THE PRESENT INVENTION
It is the first object of the instant invention to provide a natural gamma
emitter sub to be placed in the drill string in the near proximity of the
It is an other object of the instant invention to provide a natural gamma
emitter sub which is detectable by the gamma wireline logging operation
when passing through the joints of a drill string.
It is a further object of the instant invention to provide a natural gamma
emitter sub that is both personnel safe and non-controlled by the N.R.C.,
E.P.A. or D.O.T.
It is still further object of the instant invention to provide a natural
gamma emitter sub with a gamma count of between 200-1000 gamma counts/sec.
In the preferred embodiment it has been found that a gamma count of
200-1000 gamma counts per second is sufficient to overcome the surrounding
subsurface formations normally found in the Gulf of Mexico. Such
formations seldom exceed average gamma counts of 10 to 90 gamma ray counts
per second. Therefore, it is unnecessary to use higher gamma emitting
radioactive materials than the situation requires.
Almost all the naturally occurring radioactivity that is detectable by the
gamma-ray log operation comes from the three elements: potassium, thorium,
and uranium. All of which are controlled elements in their pure form.
However, it has been found that various compounds, containing such natural
gamma trace elements as uranium, potassium and thorium as there primary
ingredient, are readily available and commonly marketed for other
purposes. Such compounds have been discovered as viable substitutes as
natural gamma tag markers. i.e. Hydroxides and Nitrates of compounds
containing elements like Thorium, Cerium, Aluminum, Magnesium and Calcium.
These compositions are considered safe when stored or shipped in small
quantities. Such compounds can be prepared having the desired properties
or simply purchased off the shelf and coding the sub with the gamma count
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric quarter section view of an embodiment of the tag
marker pipe sub assemble.
FIG. 2 is an exploded view of the tag marker pipe sub assemble.
FIG. 3 is an end view of item 3 shown in FIG. 2 showing installation and
removal tool notches.
FIG. 4 is a schematic side view of a drill string utilizing a packer and
FIG. 5 is an initial subsurface gamma log and tubing collar locator.
FIG. 6 is a schematic side view of a drill string utilizing a tag marker,
packer and perforator tool.
FIG. 7 is a through tubing subsurface gamma log with tubing collar locator
showing gamma count spike created by the tag marker.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An illustrative embodiment of a method of providing a low radiation natural
gamma tag marker is shown in FIG. 1 in the form of a sub joint assembly 1
inserted into the drill string 12. The sub tool assembly 1 comprises a sub
joint body 2 for coupling into the drill string 12 having a box end with
tapered internal threads 11 and a pin end with tapered external threads 2a
and a inner sleeve 3 serving as a carrier for the gamma ray emitting
material 4. The inner sleeve 3 as better seen in FIG. 2 is grooved 9 at
each end to receive o-ring seals 6 and is further externally threaded 10
to cooperate with the internal threads 11 provided in the sub joint body 2
thereby forming a cavity between the body 2 and the inner sleeve 3. The
inner sleeve 3 is installed by a three toed spanner tool positioned in the
mating notches 8 provided at one end of the sleeves inside wall as seen in
FIG. 3. The natural gamma count emitting material contained in cellophane
packets 4 are held securely to the recessed portion of the inner sleeve 3
by teflon tape 5. At assembly, the inner sleeve 3 is inserted into the sub
joint body 2 while submerged in oil 7 allowing some quantity of such oil
to be trapped in the cavities around the gamma emitting material packets 4
thereby purging it of air and thus, reducing hydrostatics.
To use the natural gamma sub 1 it is simply placed in the tubing string at
the next joint above what ever tool joint is being used. When perforating,
the natural gamma sub would be placed at the joint adjacent to the packer
tool 13 which is directly above the perforator tool 14 as shown in FIG. 6.
In this manner when the initial casing well log chart 15 as shown in FIG.
5 is compared by over laying the through tubing log chart 16 for the same
well, the exact depth of the natural gamma sub is highlighted by the sharp
gamma count spike 19 as referenced on the tubing collar locator track 17
as seen in FIG. 7. By knowing the exact measurement from the natural gamma
sub 1 to the top shot of the perforator tool 14, the perforator's precise
location in the casing 18 is determined. As can be seen in FIG. 5 with the
average gamma count of the surrounding sub-surface formations less than
100 counts per second, a sub, such as the present invention, placed in the
string with a known emission rate in excess or 100, would be sufficient
for tag marking, in most cases.
It must be understood that although it is obvious that any gamma emitting
substance can be used as a tag marker as described herein. However,
heretofore it has not been acknowledged that such natural low gamma count
emitting materials were commercially available and could be utilized in a
satisfactory and safe manner for tag marking under such conditions.
It should also be understood that the preferred embodiment as described
herein may not be the only method of delivery possible. The sub's design
may vary, based on the job requirements, the particular substance used and
the form in which it is commercially available.